1. Field of the Invention
The present invention relates to a fuel cell system, and more specifically, relates to a fuel cell system which cuts off a supply of gas to a cathode in a fuel cell after an issuance of a power generation stop command.
2. Description of the Related Art
There is known a fuel cell system which cuts off a supply of air (gas) that contains oxygen (oxidizer) to a cathode after an issuance of a power generation stop command. In such a fuel cell system, if supply of air is not successfully cut off after a stoppage of power generating operation, there will be a problem of fuel cell deterioration caused by localized electrochemical reactions occurring in the fuel cell. In order to prevent this, it is necessary to determine whether or not the supply of air from outside has been successfully cut off after the issuance of the power generation stop command.
JP-A 2004-192919, for example, discloses a fuel cell system which determines the system's state of air-tightness based on detection results from pressure sensors after a stoppage of the power generating operation.
Also, JP-A 2006-318669 discloses a fuel cell system which determines whether or not oxidizer and fuel are supplied appropriately to a plurality of fuel cells during power generation, by making a comparison between an average of impedances in the fuel cells and an impedance in one of the fuel cells.
However, the technique according to JP-A 2004-192919 requires a plurality of pressure sensors, which results in a complicated system configuration.
The technique according to JP-A 2006-318669 determines the state of supply of the oxidizer and the fuel to the fuel cells during power generation, and does not determine whether or not the external supply of air has been cut off after a stoppage of power generating operation. The technique requires application of an AC signal to the fuel cells, which means that use of the technique according to JP-A 2006-318669 after a stoppage of power generating operation requires an external power source, etc.